We examine the effects of foreign entry on productive efficiency during the Polish investment liberalisation. The performance of foreign acquisitions is compared to foreign firms entering the market through greenfield entry, as well as domestic acquisitions of privatised firms, domestic greenfields and remaining state-owned (non-privatised) firms during the period 1995-2000. We find that foreign privatised firms have realised larger productivity gains than all types of domestic firms and that this is not due to higher price-cost margins, which is consistent with the idea that foreign firms bring in firm-specific knowledge. Foreign greenfields have the highest average labour productivity, while foreign privatisations show the largest productivity increase.